Synthetic Aperture Imaging Using High-Frequency Convex Array for Ophthalmic Ultrasound Applications.

Hae Gyun Lim,Hyung Ham Kim,Changhan Yoon

doi:10.3390/s21072275

Hae Gyun Lim, Hyung Ham Kim + Show 1 more

Open Access

https://doi.org/10.3390/s21072275

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Abstract

High-frequency ultrasound (HFUS) imaging has emerged as an essential tool for pre-clinical studies and clinical applications such as ophthalmic and dermatologic imaging. HFUS imaging systems based on array transducers capable of dynamic receive focusing have considerably improved the image quality in terms of spatial resolution and signal-to-noise ratio (SNR) compared to those by the single-element transducer-based one. However, the array system still suffers from low spatial resolution and SNR in out-of-focus regions, resulting in a blurred image and a limited penetration depth. In this paper, we present synthetic aperture imaging with a virtual source (SA-VS) for an ophthalmic application using a high-frequency convex array transducer. The performances of the SA-VS were evaluated with phantom and ex vivo experiments in comparison with the conventional dynamic receive focusing method. Pre-beamformed radio-frequency (RF) data from phantoms and excised bovine eye were acquired using a custom-built 64-channel imaging system. In the phantom experiments, the SA-VS method showed improved lateral resolution (>10%) and sidelobe level (>4.4 dB) compared to those by the conventional method. The SNR was also improved, resulting in an increased penetration depth: 16 mm and 23 mm for the conventional and SA-VS methods, respectively. Ex vivo images with the SA-VS showed improved image quality at the entire depth and visualized structures that were obscured by noise in conventional imaging.

Highlights

High-frequency ultrasound (HFUS) imaging (>15 MHz) has evolved rapidly over the last decade and opened up new applications such as ophthalmic, dermatologic, intravascular, small animal, and molecular imaging [1,2,3,4,5,6,7]. It can provide sub-millimeter spatial resolution determined by f # ·λ at the expense of a shallow penetration depth
Most custom-built or commercialized HFUS imaging systems have employed mechanically scanning single-element transducers to form an image [8,9,10]. While these single-element imaging systems have offered exciting potential for many applications, they suffered from low spatial resolution and signal-to-noise ratio (SNR) in the out-of-focus regions, deteriorating the image quality [11]
Ultrasound imaging with the synthetic aperture imaging with a virtual source (SA-VS) was illustrated and showed its potential for ophthalmic imaging

Summary

Introduction

High-frequency ultrasound (HFUS) imaging (>15 MHz) has evolved rapidly over the last decade and opened up new applications such as ophthalmic, dermatologic, intravascular, small animal, and molecular imaging [1,2,3,4,5,6,7]. It can provide sub-millimeter spatial resolution determined by f # ·λ (where f # is defined as a ratio of a focal distance to a length of the aperture used for transmission/reception, and λ is the wavelength) at the expense of a shallow penetration depth. The array transducer-based systems capable of dynamic receive focusing use electronic scanning to form an image; it provides a higher frame rate and image quality than those by the mechanical scanning systems

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